Difficulty controlling anger is a common postdeployment problem in military personnel. Chronic and unregulated anger can lead to inappropriate aggression and is associated with behavioral health, legal, employment, and relationship problems for military service members. Military-related betrayal (e.g., military sexual assault, insider attacks) is experienced by over a quarter of combat service members and is associated with chronic anger and aggression. The high level of physical risk involved in military deployments make interconnectedness and trust in the military organization of utmost importance for survival during missions. While this has many protective functions, it also creates a vulnerability to experiencing military-related betrayal. Betrayal is related to chronic anger and aggression. Individuals with betrayal-related injuries express overgeneralized anger, irritability, blaming others, expectations of injustice, inability to forgive others, and ruminations of revenge. Current approaches to treating anger and aggression in military populations are inadequate. Standard anger treatment is not trauma-informed and does not consider the unique cultural context of anger and aggression in military populations, therefore is not well suited for anger stemming from military-related betrayal. While trauma-informed interventions targeting anger for military personnel exist, anger outcomes are mixed, and aggression and interpersonal functioning outcomes are poor. Also, these anger interventions are designed for patients with posttraumatic stress disorder. However, not all military-related betrayal meets the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition-5 definition of trauma, though it may still lead to chronic anger and aggression. As a result, these patients lack access to treatment that appropriately targets the function of their anger and aggression. This manuscript describes rationale, design, and methodology of a pilot clinical trial examining Countering Chronic Anger and Aggression Related to Trauma and Transgressions (CART). CART is a transdiagnostic, transgression-focused intervention for military personnel who have experienced military-related betrayal, targeting chronic anger and aggression, and improving interpersonal relationships. The pilot study will use an interrupted timeseries design, where participants are randomized to a 2-, 3-, or 4-week minimal contact waitlist before starting treatment. This design maximizes the sample size so that all participants receive the treatment and act as their own control, while maintaining a robust design via stepped randomization. This trial aims to (1) test the acceptability and feasibility of CART, (2) test whether CART reduces anger and aggression in military personnel with a history of military-related betrayal, and (3) test whether CART improves interpersonal functioning. The primary feasibility outcome will be the successful recruitment, enrollment, and initiation of 40 participants. Primary outcome measures include the Client Satisfaction Survey-8, the State Trait Anger Expression Inventory-2, Overt Aggression Scale-Modified, and the Inventory of Interpersonal Problems-Short Version. If outcomes show feasibility, acceptability, and initial effectiveness, CART will demonstrate a culturally relevant treatment for chronic anger, the most frequent postdeployment problem, in a sample of active duty service members who have suffered a military betrayal. The DoD will also have an evidence-based treatment option focusing on interpersonal functioning, including relationships within the military and within families.